The goal of this proposal is to develop a new detector technology for digital x-ray imaging based on HgI2 polycrystalline films coupled to large area flat panel amorphous silicon (a-Si:H) thin-film transistor (TFT)-addressed readout arrays. This novel imaging detector when optimized will provide order of magnitude improvements in sensitivity to x-rays and superior spatial resolution compared to detectors utilizing scintillating phosphors coupled to a-Si:H readout arrays. The increased sensitivity of the detector will allow for a ten-fold reduction in radiation dose to a patient for an equivalent quality image. The enhancement of the spatial resolution will have a direct impact on the quality of the image, which has paramount importance in many medical diagnostic procedures such as mammography. In addition, digital capabilities will allow for convenient film-less image acquisition, retrieval, and storage. Digital image processing, computer-assisted diagnosis, and the ability to provide real time images have distinct advantages in many medical diagnostics. During Phase I of this proposal we developed techniques for highly controlled growth of polycrystalline HgI2 films in terms of their thickness, sizes of the polycrystalline grains, uniformity of layers and good electrical properties. In the Phase II effort we will finalize the HgI2 film development and construct x-ray imaging detectors using initially small commercial flat panel a-Si:H readouts (approximately 2"x2"). Then we will scale up the film growth equipment and construct large area (approximately 14" x 17") x-ray imaging detector. The film growth process will be optimized for low production cost. This new x- ray imager will be characterized and compared with current commercial detectors in terms of spatial resolution, gain, linearity, noise, uniformity, and detective quantum efficiency. The imaging capabilities will be tested in our laboratory and at UCLA School of Medicine with the use of slits and phantoms. PROPOSED COMMERCIAL APPLICATIONS: There is a strong interest in application of digital radiographic detectors for medical diagnostic applications, nondestructive evaluation of materials, x-ray diffraction of biological and other material samples, and astronomical observations. Conservative estimates are that in the medical area alone there are over 600 x-ray images produced per 1000 population per year. The proposed detectors will be highly attractive to this enormous commercial market segment due to the order of magnitude performance improvements that they will offer.